The present embodiments relate to rendering in medical imaging. For three-dimensional visualization, different rendering approaches may be used. In traditional volume rendering (e.g., direct volume rendering), each pixel of the final image is sampled along the viewing direction (i.e., rays) as a direct function of collected samples within the viewing volume. Each image sample on the viewing direction of one pixel is classified as a color sample and then composited to the final image. Direct volume rendering may be performed rapidly.
Another approach is physically-based rendering. A type of physically-based volume rendering is the Monte Carlo path tracing, which is a useful rendering technique for light transport computations, where the natural light phenomena are modeled using a stochastic process. Physically-based rendering may produce a number of global illumination effects not provided by direct volume rendering. Such effects include ambient light occlusion, soft shadows, color bleeding, and depth of field, all of which increase the realism of the produced images and improve user performance on perceptually-based tasks. Since evaluation of the rendering integral may require thousands of stochastic samples per pixel to produce an acceptably noise-free image, physically-based rendering uses more processing and is slower than direct volume rendering. Depending on the rendering parameters, rendering an image may take on the order of seconds for interactive workflows and multiple hours for production-quality images. Making alterations to the rendering in interactive workflows may be time consuming with physically-based volume rendering. In medical imaging, this use of time leads to increased costs.